London is steeling itself for more anti-capitalist protests. Is anti-globalisation a valid cause? And is violent protest ever justified? BBC News Online's Megan Lane asks Billy Bragg and other seasoned campaigners.

May Day 2001, dubbed M1 2k01 by activists, is expected to prompt protests against multinational corporations and trade bodies around the world.

Billy Bragg: No way to change the world

The cause is a rallying call to protesters from a host of disparate causes, from environmentalists to anarchists.

In London, police fear that activists will be joined by anarchist groups from abroad for riots and disruption which could last days.

Last year's event, billed as a peaceful protest, ended in mayhem as a core of protesters smashed up chain shops and restaurants, and daubed graffiti on statues and the Cenotaph. Dozens of people were arrested.

So does anti-globalisation make for a good campaigning cause? And is violence ever justified?

The media has obscured the protesters' concerns by focusing on the potential for violence, says the retiring Chesterfield MP Tony Benn.

Tony Benn: "Globalisation destroys democracy"

"Thousands of people turned up in Quebec City [to protest against the Summit of the Americas]. Yet all we saw were riot police and a few people throwing stones.

"This always happens to progressive movements. The suffragettes were denounced as violent; Nelson Mandela was described as a terrorist, and that completely obliterated their arguments."

Opposing globalisation, he says, is a just cause.

"It destroys democracy. The World Trade Organisation, the European Commission, can order us about and we can't do anything about it.

"We can vote out a government we don't like, yet we've got no control over these organisations."

The anti-capitalist movement's aims are too amorphous, says Ms Evans - one of the first women to march on Greenham Common in the 1980s.

Greenham Common protesters were committed to non-violent methods

"You need an agenda, to say what alternatives you want and how they could be achieved."

On one of the many websites run by anti-capitalists, the activists say although they do not have all the answers, "imagine what we could do if we replaced capitalism with a system based on our needs and desires, not their profits."

Ms Evans, now an MEP, says the minority out to cause havoc have discredited the entire movement.

"When people go in with the aim of attacking consumer capitalism in a city like London, that'll threaten a lot of people going about their daily lives."

Mr Waddington, an expert in protest movements, has no doubt the anti-capitalists are genuine in their concerns.

"It usually takes quite a bit of time and energy to organise a protest on this scale.

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"I have no reason to suspect that they are away-day football hooligans - and that makes them more a problem to the authorities because they do care and they don't want to compromise."

Anti-globalisation is a valid cause, says the Reading University academic, and broad enough to appeal to a wide range of people.

"If somebody's interested in animal rights, global warming or Third World debt, then they will be concerned about globalisation."

But the protesters lost a degree of legitimacy and public sympathy last May, he says.

"You can dig up Parliament Square and you're not a yob, even though it's criminal damage.

"But you start painting 'Men's toilets' on the Cenotaph, the sacred shrine to those who gave their lives, and the boundaries change completely."

The veteran socialist campaigner says violence and vandalism is not an answer. Instead, the protesters should instead try to unionise the McDonald's workforce.